The invention relates to a thermoplastic polyurethane fiber, and process of making the same, where the described fiber has good dyeability, and in some embodiments, good flame retardant properties.
While elastic fibers made of thermoplastic polyurethanes (TPU) have widened their uses and caught more attention recently in the emerging market of the textile industries, due to their many useful properties, their widespread use in applications that require dyeing have been limited. This is because TPU fibers are not easily dyeable as compared to conventional textile filaments, including those melt-spun from nylon or polyester or similar materials. Some TPU fibers may accept dye, but the dye fastness properties are typically not commercially acceptable. Other may be somewhat more dyeable by one type of dye but not by another, for example TPU fibers are generally not dyeable by common acidic and/or basic dyes.
These problems have persisted for years without any satisfactory solution and so it has become a common impression that TPU fibers can only be tinted (or stained) and not fully dyed by either acidic or basic dyes. Thus their use in applications that require dyeing have been limited.
One solution to these problems is to use solution dyes (or pigment dyes) with TPU fibers. However, solution dyes are limited by their available color shades and they are not as economical as more common dyes and dyeing processes.
Other solutions to the dyeability problems of TPU fibers include covering or blending the TPU fibers with other fibers that are more dyeable, in order to hide the lack of dyeability of the TPU fibers. However, in these situations, when such fabrics made from the covered and/or blended TPU fibers are stretched, the un-dyed or poorly dyed TPU fibers may show through the colored fiber covering or be otherwise visible in the fabric.
Thus, there is an ongoing need for TPU fibers that can be dyed, that is which have improved dyeability, especially with acidic and/or basic dyes. Such fibers would reduce, or even remove, the need for covering of thermoplastic polyurethane fibers and/or the blending of thermoplastic polyurethane fibers with other more dyeable fibers, providing a significant benefit to fabric manufactures and downstream industries that use dyed fabrics. Such fibers could be used in a wider array of applications where current TPU fibers are not suitable.
There is also an ongoing need for fibers, including thermoplastic polyurethane fibers, with improved flame retardant properties. A fiber with improved flame retardant properties could be used in applications where existing fibers, which have relatively poor flame retardant properties, cannot be used due to safety concerns and/or approval requirements for such applications.
The present invention addresses both of these ongoing needs.